The present invention provides ketones of the general formula (I): ##STR1## and physiologically acceptable salts and solvates thereof, wherein R.sup.1 and R.sup.2, which may be the same or different, each represents a hydrogen atom or a C.sub.1-6 alkyl group; Im represents an imidazolyl group of formula: ##STR2## wherein one of the groups represented by R.sup.3, R.sup.4 and R.sup.5 is a hydrogen atom or a C.sub.1-6 alkyl, C.sub.3-7 cycloalkyl, C.sub.3-6 alkenyl, phenyl or phenylC.sub.1-3 alkyl group, and each of the other two groups, which may be the same or different, represents a hydrogen atom or a C.sub.1-6 alkyl group; andA is a group of the formula (a), (b), (c), (d), (e), (f) or (g) as set forth hereinafter,and when A is the group (g), the group --COCR.sup.1 R.sup.2 CH.sub.2 Im is attached at the 2- or 4- position of the indole moiety.The compounds are potent and selective antagonists of the effect of 5-HT at 5-HT.sub.3 receptors and are useful, for example, in the treatment of psychotic disorders, anxiety and nausea and vomiting.